Thermoplastic resins, chief among these being polycarbonate resins and polyester resins employed in the household electrical appliance the office automation (OA) equipment field, have excellent mechanical and chemical properties. While they are widely used across various fields for this reason, one problem which has been cited with these resins is their poor impact-resistance at low temperatures. In addition, with respect to OA applications, better resistance to heat discoloration and hydrolysis was desired in order to be recycled.
While the addition of a graft rubber such as MBS resin is effective for improving impact resistance, resistance to heat discoloration and hydrolysis declines when MBS resin is added to polycarbonate or polyester resins.
Addition of a hindered phenol, thio or phosphorous stabilizing agent is effective for improving resistance to hydrolysis and heat discoloration. However, strength may decrease depending on the amount of agent added. In addition, when a phosphorous stabilizing agent is added to a polycarbonate resin, hydrolysis can actually be promoted. As a result, a situation results in which there are limitations placed on the amount of agent added.
Japanese Patent No. 3250050, and Japanese Unexamined Patent Applications, First Publication Nos. H1-217005 and H1-297402 disclose production methods in which heat discoloration is improved by decreasing the amount of coagulating agent used in the graft copolymer latex and controlling the pH of the washing water, and thereby the amount of remaining emulsifier, which is one cause of discoloration, is decreased. However, in these production methods, it is not possible to sufficiently improve the heat discoloration of highly fluid resins such as polycarbonate and the like.
Further, as a resin composition that is capable of providing a molded article having superior impact resistance, Japanese Unexamined Patent Application, First Publication No. 2001-172458 proposes a polyvinyl chloride resin composition that includes a graft copolymer which employs a specific butadiene content and a specific particle diameter and which is made by using sulfonate and/or sulfate. However, in the obtained polyvinyl chloride composition, only impact resistance and the external appearance of the molded article are improved.
Further, Japanese Unexamined Patent Application, First Publication No. H11-158365 proposes a composition that contains an agent for strengthening impact resistance that includes a polymer assistant that does not cause deterioration in the polycarbonate resin. However, even in this composition, it is not possible to sufficiently control the breakdown of the polycarbonate.
An object of the present invention is to provide a thermoplastic resin composition which does not lose any of its essential properties, and which enables formation of a molded article having superior impact strength, and high resistance to hydrolysis and heat discoloration.